Lateral flow diagnostic assay devices are used to detect the presence or absence of at least one specific analyte in a patient's specimen or sample. In some cases, the device is configured to generate a quantitative measure of the amount of a particular analyte. For example, reference is herein made to U.S. Pat. No. 8,753,585, which is hereby incorporated by reference in its entirety.
Lateral flow assay devices are typically defined by a non-porous substrate having a planar upper or top surface having at least three (3) major zones that are formed thereon, namely: (1) a sample addition zone, (2) a transport and detection zone, and (3) a wicking zone. The sample addition zone is typically disposed at one end of the assay device and configured to receive a sample or specimen. The transport and reaction zone, in which the reaction required for the assay occurs, is typically disposed at an intermediate location on the assay device. Finally the wicking zone, which provides the majority of the media that instills capillary flow of the received sample is typically located at an end of the assay device opposite to that of the sample addition zone. The above-noted zones are each fluidically coupled to one another and define at least one fluid flow path.
In typical lateral flow assay devices, the capacity of the assay device is accurately determined by the volume that is defined by the wicking zone. When sample is added in excess, the volume subjected to the assay will always be identical, due to the well-defined and reproducible non-porous structure of the assay device. The sample flow rate in turn can be influenced and controlled by proper selection of the dimensions of the substantially capillary media, the physical properties of the media, as well as by adjusting the chemical, biological or physical properties of the media, e.g., by coating the media with a suitable compound. In some configurations, the flow rate can also be adjusted by selecting a hydrophilic tape for covering the wicking zone of the device and adjusting the properties thereof.
One problem that is presented by existing lateral flow assay devices, once the above-noted physical structure of the device has been set, is that the physical properties of the sample or specimen, such as viscosity or density, is highly influential in determining the sample or specimen flow rate. This influence means that for varying types of samples or specimens, e.g., blood as opposed to urine, completely different physical layouts of the individual lateral flow devices must be designed in order to produce a sample or specimen flow rate that results in adequate sensitivity. The sample or specimen flow rate determines the amount of reaction time, and in general, the greater the reaction time, the greater the sensitivity of the assay.
The foregoing noted effects can thereby possibly lead to greater imprecision of assay results, due to varying reaction times. As a result, there is a general need in the field to provide an improved lateral flow assay device that is more capable of standardization.